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Thread: Guitar control trickery!

  1. #1
    Supporting Member Steve A.'s Avatar
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    Guitar control trickery!

    I just came up with three wiring tricks for Les Paul-style guitars with 2 HBs and 4 controls that are so simple that I'm embarrased that I didn't think of them years ago.

    #1. Tweaking a typical phase reverse switch [#2 & #3 to follow in first reply]

    If and when you add a phase switch to a Les Paul you will probably discover that you need to back off the volume of one pickup or the other to get a usable tone (with both volume controls set to 10 the tone is usually thin and whiny, especially if the two pickups are very similar.)

    Rather than having to turn down the volume control for one of the pickups whenever you activate the phase switch there is a simple wiring trick that will do that for you automatically: on the phase switch add a high value resistor between the normally grounded lead and ground. For example with a 500K linear pot to achieve the setting for 8 (out of 10) you would add a 2M resistor to ground. [See math in Post #2]

    With the phase switch in the normal in-phase position this resistor is ignored as the normally grounded lead (green for DiMarzio and Seymour Duncan, black for Gibson see attached PDF file) is already grounded. One downside is that with just the O-O-P pickup selected the volume will be reduced a little bit.

    When you do want that thin whiny sound you can turn down the other volume control a little bit and there it is! Turn down that volume control a little bit more if you want the O-O-P pickup to dominate the mix.

    With this wiring trick it will make a difference which pickup is wired to the phase switch for a deeper sound with more bass wire up the phase switch to the bridge pickup, for a brighter sound wire it up to the neck pickup. Although as noted above you can back off the volume control of the other pickup to reverse the balance. As they say, it's all good (an expression that I really hate because its usually not all good! * )

    BTW to get the full range of blending both pickups I switch the wires at the wiper and the CW (hot) terminal of the volume pots so that the two controls are fully independent in the middle position you can go from 100% neck pu to 100% bridge pu. The downside is that without wiring in a master volume control (or adding a kill switch) you cannot completely ground the hot terminal of the output jack: with 500K volume pots there will be at least a 500K or 250K resistance to ground there depending on the setting of the selector switch. So at high gain settings you might not be able to kill the noise by setting your volume pot to 0 and with some guitars I can still hear the pickups faintly.


    Steve Ahola

    Attached file with pickup color codes (I can't verify its accuracy as I am not familiar with most of the vendors listed)...

    guitar_humbucker_wire_color_codes_guitar_wirirng_d.pdf

    Original link:

    Guitar Humbucker Wire Color Codes | Guitar Wirirng Diagrams

  2. #2
    Supporting Member Steve A.'s Avatar
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    #2 & #3: Tweaking tone controls

    #2 & #3: Tweaking tone controls

    On many Les Pauls and other 2HB guitars I wish that the neck pickup was a little brighter and the bridge pickup was a little darker. My solutions had usually involved replacing the tone pots or caps and/or magnets. Specifically to brighten up the neck pickup I might use a higher resistance pot and/or a smaller value tone capacitor, or replace an A2 magnet with A5. To cut the highs of a bridge pickup I might try the opposite.

    I just figured out a much simpler method to brighten or darken a pickup. To brighten a neck pickup I can add a resistor in series with the 500K tone pot and .022uF tone cap to raise the net resistance. To make a bridge pickup less bright I can add a resistor between the two terminals used on the 500k tone pot (typically #1 and #2***) to lower the effective resistance.

    In the first case (to make a pickup brighter) the math for adding a series resistor is simple: just add the two values. However to determine what value resistor to add in series is more complicated — you need to interrupt the signal path to insert the resistor. You can either wire in a pot temporarily and adjust it until you find the desired brightness, or wire in jumper clips to test different value resistors.

    In the second case (to reduce the brightness of a pickup) the measurements are easier but the math is more complicated. With just two terminals used on a guitar tone pot you can determine the net resistance of your desired setting (like 8 out of 10) by subtracting the resistance between the unused terminal and the wiper (#2 and #3) from that between the outside terminals (#1 and #3). In the example below the desired net resistance of the tone control would be 400K (a 500K linear pot set to 8 of 10).

    The math for adding a resistor in parallel with the active terminals on a 500k tone pot involves computing the reciprocal of the difference between the reciprocals of 500k and the added resistor across the #1 & #2 terminals on the tone pot.@@@

    With just two terminals used on a typical treble cut tone control it is relatively simple to figure out the desired net resistance to cut the brightness of a pickup; if you want the bridge pu to be no brighter than the existing control set to, say, 8 (out of 10) first measure the resistance at that setting between the #1 & #3 terminals(A) and the #2 & #3 terminals(B). The math to determine the value resistor to add in parallel with the two terminals used (A & B) is more complicated — you must compute the reciprocal of the difference between the reciprocals of A and (A-B).

    For example, with a 500k linear pot with a desired maximum value of 8 out of 10 we would compute:
    1/(1/(A-B) - 1/A) = 1/(1/100K - 1/500K)
    To simplify matters I always drop the K in the fractions and add it to the result:
    1/(1/(500-100) - 1/500)
    = 1(1/400 - 1/500)
    = 1(.0025 - .002)
    = 1/0.0005
    = 2,000
    After adding the K suffix the answer is 2M

    Which means that we would add a 2M resistor across the #1 & #2 terminals of a 500K tone pot to make the net resistance 400K so that it would get no brighter than the existing pot set to 8 out 10.

    NOTE: By adding the resistor (called a tapering resistor) it would alter the taper of the pot a little bit. If I recall R.G.'s article correctly for a pot wired as a variable resistor it would make the taper more like a reverse audio pot. So turning down from 10 would go a little bit slower and turning up from 0 a little bit faster.


    *** When I started writing articles on guitars and amps 20 years ago I did not know that there were any standards in numbering pot terminals so I usually referred to them as Wiper, CW & CCW or Wiper, Normally Hot & Normally Cold. However one of the standard numbering schemes is that the wiper is #2, the CCW terminal (typically connected to ground) is #1 and the CW terminal (not usually connected to ground) is #3.
    Why? For one thing you can have a simple volume control with just the wiper connected to the hot signal and the CCW terminal connected to ground as I discovered in my 1939 Rickenbacher lap steel.

    In my example I used a 500K linear pot to simplify matters (a 500K pot set to 8 out of 10 will measure 100K between terminals #2 & #3.)

    @@@ Alternately you could add a capacitor in parallel with the tone cap to increase the net capacitance to make the pickup darker, or in series to decrease the net capacitance to make it brighter. Of course we all know that the math for adding caps in parallel or series is the opposite of that for resistors.


    Steve Ahola

    P.S. Replacing controls on a Les Paul is a drag because they require a special more expen$ive pot with a longer bushing to go through the carved top. If at all possible I try to adapt the existing pots for my own nefarious schemes!
    Last edited by Steve A.; 03-28-2017 at 08:40 PM.

  3. #3
    ToneOholic! big_teee's Avatar
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    My fix has always been with pickups.
    Less turns on the neck pickup, and more turns on the bridge.
    With conventional wiring. YMMV
    T
    Technicians Run the World, but Bankers, Lawyers, and Accountants, Take All The Credit!
    Keep Rockin! B_T
    Terry

  4. #4
    rjb
    rjb is offline
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    Quote Originally Posted by Steve A. View Post
    If and when you add a phase switch to a Les Paul you will probably discover that you need to back off the volume of one pickup or the other to get a usable tone (with both volume controls set to 10 the tone is usually thin and whiny, especially if the two pickups are very similar.)

    Rather than having to turn down the volume control for one of the pickups whenever you activate the phase switch there is a simple wiring trick that will do that for you automatically: on the phase switch add a high value resistor between the normally grounded lead and ground. For example with a 500K linear pot to achieve the setting for 8 (out of 10) you would add a 2M resistor to ground.
    This trick is reminiscent of Bill Lawrence's "half out of phase" wiring:
    Replace one of the "criss-cross" wires on the phase switch (typically for the neck pickup) with a ~.005uF-.02uF capacitor. The capacitor blocks bass frequencies from the neck pickup; since fewer bass frequencies are cancelled, you get a fuller sound. With the neck pickup selected and the phase switch engaged, you get a thinner, somewhat "single coil-ish" neck tone.

    Here's how it's implemented in a Tele:


    The same trick was used in the Gibson L6-S (see the .02uF cap across the selector switch terminals):
    l6-s.jpg


    -rb
    Steve A. and eschertron like this.

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